With conventional molding techniques, a common method for holding the male and female molds or dies together is to utilize a clamping device that is mechanical, pneumatic or hydraulic in its operation. These clamps are generally arranged about the edges of the molds so as to direct as even a pressure as possible to the clamping flanges. However, whenever such clamps fail due to a poor seal being made or uneven pressure being exerted about the parting surfaces of the molds, the material which is injected between the mold or dies will leak from that point thereby running on to the shop floor causing a mess and releasing sometimes dangerous fumes into the surrounding air.
Furthermore, with such conventional molding techniques, it is essential that a vent hole be provided at the apex of the mold or die. This vent hole must overflow with the injected material in order to eliminate air bubbles from being trapped in the mold cavity and thereby in the resulting injected part.
Furthermore, in the conventional method, an adequate seal of some type must be used to prevent leakage while the mold is being filled.
Although the use of vacuum in order to aid the molding process is known as is described in U.S. Pat. No. 2,913,036 and British Pat. No. 944,955, such techniques have not been utilized in standard two-piece molding processes, nor are they directly applicable to such processes.